Re: Severe netbsd-6 NFS server-side performance issues

[Hauke Fath <hf%spg.tu-darmstadt.de@localhost>]

At 14:54 Uhr -0400 04.06.2012, Thor Lancelot Simon wrote:
>On Mon, Jun 04, 2012 at 09:46:26AM -0700, Brian Buhrow wrote:
>>      hello.  From the description, it sounds like the amr(4) driver is
>> really getting wedged somewhere and this is what's causing yor problem.
>
>It sounds to me like either:
>
>A) The amr -- due to driver or firmware issues, hard to say which -- has
>   gone from writeback to write-through mode and is thus performing
>   terribly on real workloads with random read and write traffic.

It would look like this, but

# amrctl stat -v | grep Logical
Logical volume 0        optimal (1675.78 GB, RAID5
<writeback,no-read-ahead,adaptative-io>)
#

as well as the controller bios setup speak against it.

>B) If you are using "log" mode with your FFS filesystems, it may be that
>   the cache-flush transactions performed by the WAPBL code are actually
>   causing a full flush of the amr's nonvolatile cache.  If so, this is a
>   bug either in the firmware or the driver.

... which would have snuck into the netbsd-6 driver five weeks ago?

>  If the cache has optimal
>   battery state, a synchronization requested by WAPBL should not cause it
>   to be flushed to the disks.
>
>The adapter does show optimal battery status and write-back cache mode?

See above. The controller setup agrees, and is happy with the battery,
contradicting

# amrctl stat -b
Battery status          pack missing, charge unknown
#

>If so, I'd start investigating one of the two possibilities above.  I bet
>you can provoke the issue by, for example, doing a "dd" from the raw device
>with a large block size to generate a steady stream of read traffic, and
>then running postmark with the parameters adjusted to cause several minutes
>of widely scattered I/O with a lot of directory transactions.

I'll look into that - Friday is the next maintenance window...

Thanks,
        hauke


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